Changes between Initial Version and Version 1 of Sound_engine

Timestamp:

Feb 23, 2008, 4:19:00 AM (16 years ago)

Author:

trac

Comment:

--

Sound_engine

@@ +1 @@
+overview
+--------
+
+this module provides a moderately high-level sound interface. basic usage
+is opening a sound and requesting it be played; it is closed automatically
+when playback has finished (fire and forget).
+any number of sound play requests may be issued; the most 'important' ones
+are actually played (necessary due to limited hardware mixing capacity).
+3d positional sounds (heard to emanate from a given spot) are supported.
+active sound instances are referenced by Handles (cf. [wiki:handle_manager h_mgr]), so changing volume etc.
+during playback is possible (useful for fadeout).
+
+
+sound setup
+-----------
+
+OpenAL provides portable access to the underlying sound hardware, and
+falls back to software mixing if no acceleration is provided.
+we allow the user to specify the device to use (in case the default
+has problems) and maximum number of sources (to reduce mixing cost).
+
+
+performance
+-----------
+much effort has been invested in efficiency: all sound data is cached,
+so every open() after the first is effectively free. large sound files are
+streamed from disk to reduce load time and memory usage. hardware mixing
+resources are suballocated to avoid delays when starting to play.
+therefore, the user can confidently fire off hundreds of sound requests.
+finally, lengthy initialization steps are delayed until the sound engine
+is actually needed (i.e. upon first open()). perceived startup time is
+therefore reduced - the user sees e.g. our main menu earlier.
+
+
+terminology
+-----------
+
+; hardware voice : refers to mixing resources on the DSP. strictly speaking, we mean 'OpenAL source', but this term is more clear. voice ~= source, unless expensive effects (e.g. EAX) are enabled. note: software mixing usually doesn't have a fixed 'source' cap.
+; gain : is quantified volume. 1 is unattenuated, 0.5 corresponds to -6 dB, and 0 is silence. this can be set per-source as well as globally.
+; position : of a sound is within the app's coordinate system, the orientation of which is passed to snd_update.
+; importance : of a sound derives from the app-assigned priority (e.g. voiceover must not be skipped in favor of seagulls) and distance from the listener. it's calculated by our prioritizer.
+; virtual source : denotes a sound play request issued by the app. this is in contrast to an actual AL source, which will be mixed into the output channel. the most important VSrc receive an al_src.
+; sound instances : store playback parameters (e.g. position), and reference the (centrally cached) "sound data" that will be played.